Performance analysis of pulse position modulation-based hybrid technique for cellular backhaul free-space optical link

We investigate the performance of half-cosine pulse-shaped hybrid pulse position modulation-orthogonal frequency division multiplexing (HC-PPM-OFDM) under weak (i.e., log-normal) and strong (i.e., gamma–gamma) turbulence free-space optical channel. Joint impact of frequency and time offset on the performance parameters such as intercarrier interference, a symbol to interference ratio, and bit-error rate are also investigated. This research aims to improve the spectral efficiency performance of traditional PPM through the proposed hybrid technique. Further, the proposed HC-PPM-OFDM technique is compared with pulse position modulation-minimum shift keying (PPM-MSK), PPM, and hybrid PPM-OFDM. Obtained results show comprehensive improvement in the performance parameters under both weak and strong atmospheric turbulences. In addition to the above results, the upper-bound channel capacity expression is derived for log-normal as well as gamma–gamma turbulence channel models. Obtained results reveal that the proposed modulation technique outperforms PPM and PPM-MSK techniques under all turbulence conditions at a marginal cost of power penalty.